Cellulose crosslinking
is a very important textile chemical process, and is the basis for a vast array
of durable press- and crease-resistant finished textile products. N-methylol
crosslinkers containing formaldehyde give fabrics desirable properties of mechanical stability (e.g. crease resistance, anti-curl, shrinkage resistance, durable
press), but also impart strength loss and the potential to release
formaldehyde, a known human carcinogen. Other systems, e.g. polycarboxylic
acids, have been tested with varying degrees of success. We have developed
methods of forming ionic crosslinks that provide outstanding crease-angle
recovery performance, as well as complete strength retention in treated goods,
without the potential for releasing any low-molecular weight reactive
materials, such as formaldehyde. Our work is based on reactions of cellulose
with materials that impart an ionic character to the cellulose, e.g.
chloroacetic acid for negative charges or 3-chloro-2-hydroxypropyl trimethyl ammonium chloride for positive charges. These reactions produce ionic
celluloses that can then sorb a polyionic material of opposite charge to form
crosslinks. Cellulose treated with cationized chitosan after carboxymethylation
showed significant increases in crease recovery angles without strength loss.

The crosslinking of cellulose is a
crucial textile chemical process, and provides the textile manufacturer a multitude
of commercially important textile products. The most commonly used crosslinking
systems are based on N-methylol chemistry. These crosslinkers give fabrics many
desirable mechanical stability properties (e.g. crease resistance,
anti-curl, shrinkage resistance, durable-press), but also impart strength loss
and the potential to release formaldehyde, a known human carcinogen. [4] Other
chemical systems that do not contain formaldehyde, e.g. polycarboxylic acids,
have been explored with varying degrees of success.[9,10] In this work we
report on methods of forming ionic crosslinks, rather than the typical covalent
crosslinks, to provide crease-angle recovery performance without formaldehyde
release.

Ionic cellulose can be produced with a variety of reagents. Figure 1 provides examples of obtaining anionic cellulose
by reacting chloroacetate with cellulose and cationic cellulose by a similar
reaction with 3-chloro-2-hydroxypropyl trimethyl ammonium. These reactions produce ionic celluloses that can then sorb a polyelectrolyte of opposite charge to form
crosslinks.

There are numerous strategies for producing ionic crosslinks. In this work, we will discuss the use of cationized chitosan to
crosslink cotton which has been made anionic with chloroacetate.

The reaction of chitosan with
3-chloro-2-hydroxypropyl trimethyl ammonium leads to a cationized polymer that
maintains its cationic character regardless of pH (Figure 3).